Hydroxyapatite and Other Biomedical Coatings by Electrophoretic Deposition - Biological and Biomedical Coatings: Processing and Characterization - page 82

Introduction
In his extensive review of bioceramics, Hench [1] indicated that one of two primary clinical
applications of porous ceramics was in the form of hydroxyapatite coatings for (1) prostheses
as alternatives to cement fixation and (2) dental implants for bioactive fixation. Although
there are many reports of methods that can be used to fabricate thin (and thick) films of
ceramics on the surfaces of substrates and their properties, the most common types of
fabrication can be categorized generally according to Figure 3.1 [2-17].
The focus of the present work is electrophoretic deposition , particularly of hydroxyapatite
(Ca 10 [PO 4 ] 6 [OH] 2 ), which is one of two well-known analogs of electrodeposition [18,19]:

• Electrolytic deposition: surface coating produced from dissolved ions or complexes
• Electrophoretic deposition: surface coating produced from suspended particles

Table 3.1 [20,21] summarizes the differences between these two techniques for surface
coating application.
Although electrolytic deposition is well known as the process by which metals are plated
on other metals, there has been a number of reports of the use of this technique to produce
ceramic coatings, including Al 2 O 3 , TiO 2 , and hydroxyapatite [19].
In electrophoretic deposition, what are typically colloidal particles are deposited onto a
conductive substrate in the presence of an external electrical field [20,22]. These particles,
which are conductive owing to surface electrical charge, migrate to the substrate of oppo-
site charge, and so particle deposition may occur either on the cathode or anode. Generally,
any solid that can be suspended, typically in the form of a powder less than ~30 µm in size,
can be used for electrophoretic deposition [19,23]. This process is applicable to many types
of materials, including oxides, carbides, nitrides, glasses, metals, and polymers.

in film coatings

Chemical methods Physical methods

Solid
source

Liquid
source

Solid
source

Suspension
source

∙ Sputtering
∙ Pulsed laser
deposition
∙ Molecular
beam epitaxy

∙ Evaporation
∙ Atomic layer
epitaxy

∙ Evaporation
∙ Sol-gel spin
casting
∙ Sol-gel
dip-coating
∙ Spray pyrolysis
∙ Gel oxidation
∙ Anodic oxidation

∙ Electrophoretic deposition (EPD)
∙ Dipcoating
∙ Sol-gel screen printing
∙ Aerosol spraying
∙ Tape casting

FIGURE 3.1
Summary of fabrication methods for ceramic thin films.